Lecture 13 Flashcards
(31 cards)
what are PFAS?
- group of over 9000 synthetic chemicals that have been used in industry and consumer products for over 70 years
- a group of organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain with a hydrophilic functional group
what are the characteristics of PFAS?
- carbon-fluoride bond, one of the strongest bonds in organic chemistry
- exhibit high resistance to degradation and heat, thus can be very persistent in the environment with degradation periods of years, decades, or longer
what are PFAS uses?
broad range of consumer products:
- food packaging
- nonstick cookware
- stain resistant fabrics and carpets
- some cosmetics
- firefighting foam
what were PFAS manufactured and when did they appear in the environment?
- manufacturing began in the 1940s
- first detection in wildlife was reported 50 years later
what do PFAS bind to?
proteins = proteinophilic
what are PFAS branded as?
- forever chemicals
- PFOS and PFOA are generally referred to as ‘legacy PFAS’
groups of PFAS include:
- PASs
- PFCAs
- PFSAs
- FTOH
- PFAAs
what are physico-chemical characteristics of PFASs?
- resistance to both environmental and biological degradation
- thermal and chemical stability against oxidation, photolysis, and hydrolysis reactions
- hydrophobicity
- oleophobicity (resistant to the penetration of oils)
what is the relationship between PFASs and the stockholm convention?
3 PFASs have been listed under the stockholm convention:
- PFOA, its salts, and PFOA-related compounds = annex A
- PFOS, its salts, and POSF = annex B
- PFHxS, its salts, and PFHxS related compounds = annex A
- in 2021, long chain PFCAs and their precursors have also been proposed by the canadian government for inclusion in the stockholm convention
what are 3 exemptions under status B for PFOS?
- photo imaging
- aviation hydraulic fluids
- firefighting foam
what are unregulated PFASs?
- GenX chemicals (a group used as substitutes for PFOA and PFOS)
- FTOH
- PFBS: a shorter chain PFAS (C>/= 6) used in various applications, remains unregulated for the most part
what are PFAS replacement products?
short-chain PFBSs:
- Technical performance is lower than that of long chain PFHxS and PFOS
- Much larger quantities of PFBS have thus been used to achieve a similar performance to PFHxS and PFOS
- Short-chain PFASs are highly mobile in the water bodies
- Final degradation products are extremely persistent
- A lack of regulations and proper water treatment techniques for short-chain alternates will bring about the never-ending existence of these contaminants in the aqueous environment
what are sources of PFAS to the marine environment?
- PFAS production sites, such as chemical industries
- Improper disposal practices, often originating from
nonpoint sources and runoff from landfills
containing PFAS - Inland activities (e.g., biosolids) are another
significant contributor to PFAS pollution in marine ecosystem as they can introduce PFAS into the marine environment through riverine discharges - Volatile PFAS can be transported through the atmosphere, serving as another major source of PFAS contamination in marine and terrestrial
environments
how are PFASs transported via atmospheric transport?
- PFASs are known to undergo long-range transport to remote environments such as the Arctic via oceanic or atmospheric transport
- Mechanism remains largely unknown
- Neutral PFASs (e.g., FTOHs, FOSEs, FOSAs)
are more volatile and less water soluble than PFAAs and are susceptible to long-range atmospheric transport to the Arctic - Neutral PFASs can be degraded in the atmosphere to form ionic PFAAs and
subsequently deposit via wet or dry atmospheric deposition
how do PFAS partition?
- Short-chain PFASs more dominant in
the water and can form up to 88.8% of
the total PFAS concentration in water - Long-chain PFASs more dominant in
the sediment and SPM (suspended
particulate matter)
what are the human health affects of PFASs?
- Nearly all Canadians carry low levels of
perfluorinated chemicals, including PFOS, in their blood as a result of exposure - ƩPFAS35 drinking water limit (Canada): 30 ng/L
- ƩPFAS20drinking water limit (EU): 100 ng/L
- PFOS and PFOA: 4 ng/L for each (USEPA)
- Half-life in humans range from 2.3-7.3 years
- Immunosuppression, neurological disorders, cancer
how are PFASs directly vs. indirectly emitted into the environment?
- directly: manufacture, use and disposal of products containing PFASs
- indirectly: abiotic or biotic degradation of their precursors/ the production of persistent metabolites such as PFOS
how do PFASs transport within an organism?
- molecules enter the organism and reach various tissues through blood circulation
- PFASs contain a terminal acidic group and a long highly hydrophobic carbon chain. due to their structural similarity to fatty acids, PFASs are able to competitively bind to various transport proteins
what are the toxic effects of PFASs?
- they are primarily mediated by their binding to proteins, nuclear receptors, and membranes
- eg. PFASs can regulate PPAR signalling by binding to the classical ligand-binding pocket in the receptor or by interacting with its allosteric binding sites
what are transport proteins?
- play important roles in the distribution and accumulation of PFASs in the body
- HSA is responsible for the transport of PFASs in blood circulation
- L-FABP is responsible for the entry of PFASs into the liver
- NTCP then carries PFASs from the liver to bile, from there PFASs are absorbed into the intestinal epithelial cells following the same mechanism as bile acids
PFAS marine mammal tissue accumulation:
- PFOS was first reported in tissues of 15 marine mammal species collected worldwide in 2001
- highest concentrations of PFAS are found in the livers followed by kidneys in fish and marine mammals
PFAS contamination in the arctic:
- polar bears, the apex predator in arctic regions, have been found to be among the most contaminated wildlife
- these chemicals cross the blood-brain barrier of bears, and inner regions of the brain contain high concentrations of PFASs
- long chain PFCAs (C11-15) and PFOS was found to be predominant in the brain of bears
PFAS contamination at the poles:
- PFOS and long chained PFCAs (C9-12) have been detected in canadian arctic and greenland ringed seals
- FOSA was a dominant PFAS detected in alaskan beluga whales between 1989-2006
are contaminants transferred to offspring?
- yes, PFAS has been found to be transferred from mother to fetus in marine mammals
- transplacental transfer rates of PFCs were higher than those for PCBs and PDBEs
- PFOS concentrations in harbour seal pups were 2.6-fold higher than those in adult females, suggesting the importance of maternal transfer
- PFC concentrations in female bottlenose dolphins that haven’t been observed with calves were greater than those with calves, suggesting an off-loading effect
- PFCs were detected in milk samples, confirming transfer of PFCs through lactation
